Start by gathering all your ingredients. Ensure the cream cheese is softened for easy mixing, and preheat your oven to 350°F (175°C). Grease your 9x13 inch baking pan or line it with parchment paper for easy removal later.
In a large mixing bowl, combine the devil's food cake mix, 1 egg, and 8 tablespoons of melted butter. Mix until well combined and smooth. The batter will be thick; that’s perfectly normal!
Pour the cake batter into your prepared baking pan. Use a spatula to spread it evenly across the bottom of the pan. This will create the perfect foundation for your gooey filling.
In another mixing bowl, beat together the softened cream cheese and 1 cup of Nutella until smooth. Add in the 3 eggs and 1 teaspoon of vanilla extract, mixing until fully incorporated. Finally, drizzle in the 8 tablespoons of melted butter and gradually add the powdered sugar, mixing until the filling is creamy and well blended.
Carefully pour the Nutella filling over the cake base in the baking pan. Use a spatula to spread it evenly, ensuring the filling covers the entire surface of the cake batter.
Place the pan in the preheated oven and bake for 40-45 minutes, or until the edges are set but the center remains soft and gooey. Be careful not to overbake; the gooey texture is essential for this recipe.
Once baked, remove the cake from the oven and allow it to cool in the pan for about 20 minutes. After cooling, slice into squares and serve warm or at room temperature. A dusting of powdered sugar on top adds a lovely finishing touch!
